The present invention relates generally to a rotor having a super-conductive coil in a synchronous rotating machine. More particularly, the present invention relates to an enclosure for such a rotor.
Synchronous electrical machines having field coil windings include, but are not limited to, rotary generators, rotary motors, and linear motors. These machines generally comprise a stator and rotor that are electromagnetically coupled. The rotor may include a multi-pole rotor core and coil windings mounted on the rotor core. The rotor cores may include a magnetically-permeable solid material, such as an iron-core rotor.
Conventional copper windings are commonly used in the rotors of synchronous electrical machines. However, the electrical resistance of copper windings (although low by conventional measures) is sufficient to contribute to substantial heating of the rotor and to diminish the power efficiency of the machine. Recently, super-conducting (SC) coil windings have been developed for rotors. SC windings have effectively no resistance and are highly advantageous rotor coil windings.
High temperature SC coil field windings are formed of super-conducting materials that are brittle, and must be cooled to a temperature at or below a critical temperature, e.g., 27xc2x0 K., to achieve and maintain super-conductivity. The SC windings may be formed of a high temperature super-conducting material, such as a BSCCO (BixSrxCaxCuxOx) based conductor.
In addition, high temperature super-conducting (HTS) coils are sensitive to degradation from high bending and tensile strains. These coils must undergo substantial centrifugal forces that stress and strain the coil windings. Normal operation of electrical machines involves thousands of start-up and shut-down cycles over the course of several years that result in low cycle fatigue loading of the rotor. Furthermore, the HTS rotor winding must be capable of withstanding 25% overspeed operation during rotor balancing at ambient temperature and occasional over-speed at cryogenic temperatures during operation. These overspeed conditions substantially increase the centrifugal force loading on the windings over normal operating conditions.
HTS coils used as the rotor field winding of an electrical machine are subjected to stresses and strains during cool-down and normal operation as they are subjected to centrifugal loading, torque transmission, and transient fault conditions. To withstand the forces, stresses, strains and cyclical loading, the HTS coils must be properly supported in the rotor. These support systems and structures that hold the coils in the rotor should secure the coils against the tremendous centrifugal forces due to the rotation of the rotor. Moreover, these support systems and structures should protect the HTS coils and ensure that the coils do not crack, fatigue or otherwise break.
Developing support systems for HTS coil has been a difficult challenge in adapting SC coils to rotors. Examples of HTS coil support systems for rotors that have previously been proposed are disclosed in U.S. Pat. Nos. 5,548,168; 5,532,663; 5,672,921; 5,777,420; 6,169,353, and 6,066,906. However, these coil support systems suffer various problems, such as being expensive, complex and requiring an excessive number of components. There is a long-felt need for a rotor and coil support system for a HTS coil in a synchronous machine. The need exists for HTS coil support system made with low cost and easy-to-fabricate components.
In a first embodiment, the invention is a rotor for a synchronous machine is disclosed having: a rotor core having a rotor axis; at least one super-conducting coil winding arranged around the rotor core; at least one pair of coil support beams attached to the coil winding and secured to the rotor core, wherein said coil support beams are separated from the rotor core, and a cold coil support cylinder fitted over an outside surface of said beams.
In another embodiment, the invention is a rotor for a synchronous machine comprising: a rotor core having a rotor axis; at least one super-conducting coil winding mounted on the rotor core; at least one pair of coil support beams having an inner slot support the coil winding, said beams symmetrically arranged around the core, and said beams separated by a gap from said core, and a plurality of torque rods spanning and connecting opposite coil support beams, wherein said torque rods are offset from and symmetrically arranged about an axis of the rotor.